Heat treatment and heat-treating furnace



Sept. 17, 1940. J. N. WILSON HEAT TREATMENT AND HEAT-TREATING FURNACE Filed Feb. 1, 1939 INVENTOR UNITED STATES PATENT OFFICE HEAT TREATMENT AND HEAT-TREATING FURNACE- John N. Wilson, Washington, Pa., assignor to Frazier-Simplex, Inc.

ware

, a corporation of Dela- Application February 1, 1939, Serial No. 253,997

1 Claim.

The invention relates to heat treatment, and consists in improvement in the heat-treating furnace. The object is to gain more accurate control of the temperature gradient through which the article under treatment passes as it advances on its course through the furnace. The invention has been developed in the annealing of articles of glassware, and in that application it will be particularly described; but since it centers in the control of the temperature gradient of the article under treatment, the invention is not necessarily connected with nor limited to the treatment of glassware, but is applicable in the heat treatment of articles generally.

In the accompanying drawing Fig. I is a view in vertical and longitudinal section of a leer for glassware that embodies the invention, and Figs.

II, III, and IV are views in vertical and transverse section, the plane of Fig. I is in Fig. IV indicated by the line I-I, and the planes of section of Figs. II, III, and IV are indicated by the lines 11-11, IIIIII, and IV--IV, Fig. I.

The leer of the drawing is of the open-fired tunnel type. It is a long tunnel-like structure, suitably supported. Throughout the tunnel extends the upper reach of an endless belt conveyor that, as the leer continues in operation, moves slowly in advance from the intake end, on the left, Fig. I, to the delivery end, on the right. The articles to be annealed are placed on the conveyor at the intake end of the tunnel and are ultimately discharged at the delivery end. As they advance through the tunnel they are during appropriate intervals of time subjected to those temperature condiitons that effect annealing. A stream of hot gases is maintained, flowing in the tunnel in the direction in which the conveyor travels and within this stream the advancing article of glassware passes through the desired temperature gradient. Emerging from the stream of hot gas, the article enters a stream of air, and in that stream it is cooled to normal atmospheric temperature.

The furnace of the drawing is typical in that from the intake end to an intermediate point the tunnel is formed with heat-insulating walls, and from such intermediate point to the delivery end with heat-radiant walls. The heat-insulating portion is indicated by the numeral l, the heat-radiating portion by Z; the intake is indicated at 3; the discharge at 4. The conveyor is indicated at 5. This conveyor is suitably supported, so that throughout the extent of its ware-sustaining reach it is spaced at an interval above the floor of the furnace; and it is pervided for the generation of flame. As shown in Figs. I and II, adjacent the intake end, combustion passages 6 extend transversely within the structure, beneath the floor of the tunnel. Each of these passages is closed above by a thin screen I of tile, relatively permeable by heat, that here forms the tunnel floor. To each passage, at one end, a burner opening 8 leads, and at the opposite end the passage is continued in a duct 9 that leads vertically through the side wall and that opens to the tunnel at the roof. The side-wall duct on the tunnel side is formed by a screen ill of tile, similar to the floor-screen 1. It will be understood that the successive passages 6 with their burner openings and delivery ducts are oppositely arranged, so that, the flow in one being from right to left, as indicated'in Fig.'II, the

exit a stack I2 is associated, to maintain a draft of hot gases of combustion, from the fire box through the intermediate reach of the tunnel to the exit. Beyond the exit H, to the right, Fig. I, the thickness of the heat-insulating walls of the tunnel is diminished, and beyond the portion of reduced wall thickness the tunnel Walls are, as has been said, heat-radiating. And in that portion the walls are formed, ordinarily, of sheet metal. vided, for controlling and adjusting stream-flow.

In operation a stream of hot gases is maintained flowing from left to right, Fig. I, from the intake end of the tunnel to the intermediate exit to the stack; and, the tunnel being open-ended, a stream of cold air necessarily is induced flowing from the delivery end to the exit and thence out through the stack. The opposite flow of cold perature: the hot stream that flows from left to right is growing cooler; the cold stream that flows from right to left is growing Warmer. Through these oppositely flowing streams the Dampers are commonly proware upon the conveyor 5 advances in left to right course. 7

The furnace and its operation, as thus far particularly described, are typical; and my invention consists in refinements that remain to be dwelt upon.

In the heat treatment of articles generally in such a furnace there is a temperature gradient through which the article must pass. It must (with certain margins of tolerance) be brought within a certain time interval to a certain peak temperature, then cooled within a certain time interval through a certain critical range, and after that brought to normal atmospheric temperature. The time intervals, manifestly, are determined by furnace dimensions and conveyor speed in relation to temperature conditions temperature conditions are determined by the nature of the gaseous fuel mixtures used, in relation to furnace structure and material. In the 'case of glassware the temperature cycle for annealing varies, in detail, with quality of glass and the size and the shape of the article and the distribution of its mass. A specific article is a glass milk bottle. The glass commonly employed and size andproportions are such that the peak temperature should be approximately 950 F. To "this peak the bottle (ordinarily hot when introduced at the intake 3) must within a certain interval of conveyor advance be brought. This heating must be accomplished with such slowness and thoroughness that, throughout the thickness of the walls of the bottle, the high peak temperature shall be substantially uniform. Then slovvly the article in its further advance must be cooled through the critical range of 950-800 F. When the cooling article has come to a temperature of 800 it is safe from the development within its substance of weakening strains, and from that degree downward it may be cooled more rapidly; and, for economic reasons should, within a furnace of reasonable length, be brought to. the discharge 4 at a temperature that permits of ready handling, and is not so far above normal atmospheric temperature as to render it liable under factory conditions to great and sudden :chilling. Anytemperatures mentioned are approximate and will vary according to the compo- .sitionofthe glass.

Such furnaces necessarily are installed beneath the roofs of factory buildings, and the stacks necessarily rise in the open, and the surrounding atmosphere is necessarily variable in condition, with changes of weather and of season. The relatively hot gases of combustion and the relatively cold air flowing in opposite directions to the exit from tunnel to stack necessarily, as I have perceived, overlap in the'region of meeting: the relatively hot gases of combustion tend, as I have perceived, to creep along the roof of the tunnel, and the relatively cold air tends to creep along the floor. Such a stratification is made more pronounced by the presence of the conveyor. Beneath the conveyor, and accordingly immediately beneath the ware, the enveloping body of atmosphere is, in such furnaces as have heretofore been constructed, definitely colder than the atmosphere above. This condition is prejudicial, because the mass of a bottle is generally greatest at the base, and there particularly temperature changes should be gradually effected. And it is further prejudicial because, under changing conditions of weather and season this creeping of cold air along the floor of the tunnel is of varying effectiveness, and introduces into factory procedure an indeterminable and (but for my invention) an uncontrollable factor. Furthermore, there is a swirling and eddying of the meeting streams that is variable and disturbing in its variability. The consequence and effect of these things is that in the course of prolonged operation an appreciable fraction of furnace output is damaged or ruined. It is to reduce loss on such account that my invention is intended.

I form the exit in the floor of the tunnel; I make it extensive, longitudinally of the tunnel and (preferably) laterally as well. I provide a succession of passages leading from the tunnel to the stack, and provide them severally with dampers. Thus I subject the stratum of relatively cold air that tends to creep along the floor of the tunnel to a draft that sweeps it in a direction away from the ware, away from the over.- lying stratum of relatively hot gas, and in a direction out from the tunnel to the stack. This draft draws the stratum of relatively hot gases that tends to creep along the roof of the tunnel downward, causing these gases on their Way to the exit wholly to envelop the ware. By these means the annealing operation is relieved of serious disturbance, by reason of changes in weather and season, and furnace loss is reduced.

Referring again to the drawing, and particularly to Fig. I, the exit ll will be seen to cons'ist of a succession of orifices that open through the floor at successive points in the longitudinal extent of the tunnel. The exit orifices as a group will be seen to be arranged'within the portion of the tunnel most heavily insulated, and as a group to be situated in down-stream position relatively to the group of ducts 9 through which the hot gases have ingress to the tunnel. Immediately beyond the last of these exit orifices it will be observed that the Weight of insulation of the tunnel walls is reduced.

Referring to Figs. III and IV it will further be seen that these orifices II are advantageously arranged in transverse rows; that within each row the orifices are symmetrically placed with respect to the longitudinal mid-line of the floor,

and that as between successive'rows the spacing is varied. The orifices open to passages l4 that lead beneath-the floor and through the side walls to headers I 5, whence there is uptake IE to the stack- H. In the several passages 14 adjustable dampers H are set.

It will be perceived that, in consequence of the formation of the exit as a plurality of passages leading through the floor, arranged at intervals longitudinally ofthe tunnel, the temperature gradient downward is more minutely determined and more accurately controlled.

In operation the hot gases of combustion flow in a stream from ducts 9 in left-to-right direction (Fig. I), filling the tunnel. An oppositely moving stream of relatively cold atmospheric air is induced that enters the tunnel at the delivery end (the right-hand end). In the region of meeting the cold air tends to seek the fioor of the tunnel; the hot gases, the roof. The draft induced by the stack draws the cold air downward,

burning heat-treating tunnel furnaces generally.

I claim as my invention:

In an annealing furnace of open-fired tunnel type and including from intake to delivery end. successive portions of heavily insulated walls and less heavily insulated walls, a gas-permeable conveyor spaced at an interval above the floor of the furnace and in operation advancing from intake to delivery, means for introducing hot gases in the heavily insulated portion of the furnace and at the intake end thereof, and draftinducing means adapted to induce draft both of hot gases from the intake end of the furnace and of cold air from the delivery end, said draftinducing means including an exit for gas and air arranged in the floor of the furnace, the improvement herein described which consists in such exit arranged Wholly within the heavily insulated portion of the furnace and at the delivery end thereof, whereby the ware advancing upon the conveyor, swept by downwardly streaming hot gases, comes to peak temperature within the heavily insulated portion of the furnace and 10 begins to cool as it passes into the less heavily insulated portion.

JOHN N. WILSON. 

